1. Field of the Invention
The present invention relates to a vibration motor for transmitting call information, etc. by sensible vibration built into a pager, wristwatch, portable telephone, etc. More particularly, the invention relates to a vibration motor of a structure suited for mounting on the surface of a printed circuit board.
2. Description of the Related Art
In the past, the vibration motors used for portable telephones and other telecommunications apparatuses have, for example, as shown in FIGS. 6A-6C, been comprised of a substantially tubular vibration motor body 1, a substantially half moon-like conical eccentric ring 2 tightly fixed to a motor shaft 1a projected from one end of the body 1, and lead wires 3 and 3 tightly connected to an internal terminal at an end bracket 1b of the other end of the motor body 1 by solder 1c.
When mounting such an eccentric ring type vibration motor on the printed circuit board built into a portable telephone set etc., usually use is made of, for example, a metal holder frame 5 as shown in FIG. 7. This metal holder frame 5 is provided with a rectangular bottom plate portion 6 which contacts the surface of the printed circuit board, a pair of curved spring holding pieces 7 and 7 which are bent upward from the left and right long sides, receive a substantially tubular drum portion of the vibration motor body 1, and grip the same, and engagement pieces 8 and 8 which are bent downward from the short side ends of the bottom plate portion 6 and are inserted into penetration type engagement holes of the printed circuit board.
In mounting the vibration motor to the board, first the substantially tubular drum portion of the vibration motor body 1 is fitted into the accommodation portion 9 between the curved spring holding pieces 7 and 7 to fix it in place, then the engagement pieces 8 and 8 of the metal holder frame 5 are inserted into the penetration engagement holes of the printed circuit board and the engagement pieces 8 and 8 are affixed at the rear side of the board. Then, the front ends of the lead wires 3 and 3 are affixed to the terminal pattern of the board by soldering.
In a vibration motor, however, there are the following problems.
&lt;1&gt; In order to facilitate the work of mounting on the board, it has been studied to eliminate the engagement pieces 8 and 8 of the metal holder frame 5 and the penetration engagement holes of the board and mount the parts of the vibration motor on the surface in the same way as the principal electronic components all together are mounted by reflow soldering. When adhering the bottom plate portion 6 of the metal holder frame 5 accommodating the vibration motor body to the reverse surface pattern of the printed circuit board by coating a cream solder, adhering the principal electronic components to the front surface pattern of the printed circuit board by coating a cream solder, and reflowing the solder on the printed circuit board in such a state in a heating furnace with the principal electronic components facing up to affix them, since the vibration motor is a heavy part which, even though small in size (for example, having a diameter of 7 mm and a length of 2 cm), is provided with an eccentric ring 2 having a high specific gravity, such as tungsten, only the lower side metal holder frame 5 accommodating the vibration motor body ends up detaching from printed circuit board. Of course, if the heating is carried out in a state with the metal holder frame 5 at the top side, its detachment can be prevented, but the principal electronic components themselves require stricter mounting precision, therefore there is the danger of slight floating or deviation occurring at the connection positions if the principal electronic components are faced downward. Accordingly, the metal holder frame 5 accommodating the vibration motor body must be positioned faced downward during the heating.
For this reason, the metal holder frame 5 is still provided with the engagement pieces 8 and 8 for attachment to the printed circuit board, so an additional step of attaching only the metal holder frame 5 accommodating the vibration motor body to the printed circuit board is necessary. This makes the process of mounting on the board more troublesome and causes an increase of the manufacturing cost.
&lt;2&gt; There is a method in which adhering only the metal holder frame 5 to the reverse surface pattern of the printed circuit board by coating a cream holder and affixing it in a heating furnace, then inserting the vibration motor body into this affixed metal holder frame 5 to fix it in place. However, the additional step of mounting only the vibration motor body is necessary. In the same way as that described above, it makes the process of mounting on the board more troublesome and causes an increase of the manufacturing cost.
&lt;3&gt; Further, although the mounted vibration motor is relatively strongly gripped by the curved spring holding pieces 7 and 7 of the metal holder frame 5 affixed to the printed circuit board, when the vibration motor is being started up, a relatively slight deviation is apt to occur with the spring holding pieces 7 and 7 due to the added vibration shock which it generates by itself. For this reason, when the vibration motor is repeatedly activated many times during long years of use, the slight deviation gradually accumulates and results in a situation where the vibration motor turns from its fixed position, therefore easily causes abnormalities in vibration and poor lead connection due to the tensile stress applied to the lead wires 3 and 3.